tests/shader_runner: Miscellaneus fixes.
This MR includes:
- A fix to a comment in vkd3d-shader/ir.c (out of MR scope but really tiny!).
- A fix when creating UAV buffers in the shader_runner d3d12 backend.
- Fixes to (hopefully) all the memory leaks in the shader_runner reported by valgrind when running all tests.